The new API works on normal databases (by deleting data based on the
subquery) and also on MySQL (by deleting the data using a weird join
on the subquery).

Eloy Lafuente authored Oct 14, 2020 and Sara Arjona committed Oct 14, 2020

Before there is a conversation, messages between users are sent
using core_message_send_instant_messages instead of
core_message_send_messages_to_conversation.

That method had an undefined $errormessage variable, ultimately
causing the problem detected on message_post_message()/message_send()
to never been returned by the external.

This just adds the same error than already existing conversations do,
but returning it as warning, for BC, JS will show it.

Credit goes to Helen Foster for the improvement, thanks!